1. Field of the Invention
The invention relates to a control apparatus for a hybrid vehicle, a hybrid vehicle, and a control method for a hybrid vehicle, in which, of an internal combustion engine and a motor, the internal combustion engine is configured to be intermittently operated.
2. Description of Related Art
In an internal combustion engine mounted on a vehicle, conventionally in-cylinder injection, i.e., direct fuel injection into a cylinder is finely controlled and port injection is used in combination. Fuel efficiency, an output, and combustion stability during a warm-up are improved by controlling the in-cylinder injection and the port injection. In such an internal combustion engine, the combustion in the cylinder is retarded to such a degree that the combustion is performed in the exhaust stroke by significantly retarding ignition timing. Thus, by retarding the combustion in the cylinder, an exhaust temperature is increased and a catalytic converter for exhaust gas purification is rapidly warmed up (hereinafter this warm-up is referred to as a catalyst rapid warm-up).
On the other hand, in recent years, a following hybrid vehicle has become prevalent. In the hybrid vehicle, a reduction in idling time and energy regeneration are performed by using the internal combustion engine and a motor (inclusive of a generator) in combination, and thus a significant reduction in fuel consumption has been realized. As a result, in the hybrid vehicle, the internal combustion engine can be reduced in size. In addition, the hybrid vehicle in which, by running with the motor under a running condition that the efficiency of the internal combustion engine is reduced, the intermittent operation of the internal combustion engine during the running is executed and the effect of reducing the fuel consumption is thereby enhanced is becoming prevalent. Further, the hybrid vehicle in which the fuel efficiency and exhaust gas purification performance are improved by using the internal combustion engine configured to perform the in-cylinder injection is also becoming prevalent.
Incidentally, when the cooling system of the internal combustion engine is stopped at the same time as the stop of the internal combustion engine, a fuel vapor becomes likely to occur in the fuel supply system of the internal combustion engine. For example, when the fuel vapor becomes likely to occur, a low-pressure fuel pump in the fuel supply system is driven by the motor. By driving the low-pressure fuel pump, a fuel pressure level higher than the vapor pressure level of the fuel is secured and the occurrence of the fuel vapor is thereby reduced.
In addition, during a temporary stop due to the intermittent operation of the internal combustion engine, the low-pressure fuel pump is stopped and a required fuel pressure is secured when the internal combustion engine is restarted after the temporary stop. At this point, in order to secure the required fuel pressure, the opening of an electromagnetic relief valve connected to a high-pressure delivery pipe is prohibited. On the other hand, during the stop of the internal combustion engine when the operation thereof is ended, the leakage of the fuel by opening the electromagnetic relief valve is allowed such that the fuel is not leaked from a fuel injection valve by a temporary increase in temperature due to the stop of the cooling system.
However, in the control apparatus for a hybrid vehicle described above, the internal combustion engine is intermittently driven and the frequency of repetition of driving and stopping becomes relatively high. As a result, especially in cases shown below, the high-pressure side fuel pressure tends to be reduced.
For example, there are cases where an orifice leak mechanism is used in combination with a pressure control valve. The pressure control valve limits the pressure of the fuel discharged from a high-pressure pump to a set high pressure and maintains the pressure at the set pressure. For example, the pressure control valve is a relief valve or a pressure regulator. The orifice leak mechanism prevents fuel leakage from the fuel injection valve during high-temperature soak. Alternatively, there are cases where the orifice leak mechanism that replaces the above pressure control valve is used. In such a configuration, the high-pressure side fuel pressure has tended to be reduced every time the intermittent stop is performed.
As a result, when the internal combustion engine is restarted after the temporary stop due to the intermittent operation, there has been a possibility that the fuel pressure increase for injecting the fuel required for the catalyst rapid warm-up into the cylinder is retarded. With the retardation, there has been a possibility that a fluctuation in air-fuel ratio (what is called an air-fuel ratio variation) or an interruption of the in-cylinder injection is caused and the catalyst rapid warm-up is adversely affected.
In addition, in a case where the in-cylinder injection and the port injection are used in combination as well, when the internal combustion engine is restarted after the temporary stop of the internal combustion engine due to the intermittent operation, the fuel injection amount of the in-cylinder injection fluctuates. As a result, similarly to the above case, there has been a possibility that the catalyst rapid warm-up is adversely affected.